Mk 12 build advice

[USMC-03XX]

So to start off I’m not planning on ever running this suppressed. I have no preference of 18” or 16”, was leaning towards 16” because I like the balance. And prefer short. But if there’s legit reasons to go rifle length gas and 18” over mid 16” please educate me. Barrel is coming from centurion, my main question is about the barrel nut/handguard selection. I could care less about a true 100% clone. I don’t like quad rails, had them my entire career. Fat as fuxk. But that’s only because I’ve become spoiled with mlok since retiring. So my question is, if I run a Midwest industries rail vs a geissele rail, will it effect accuracy or reliability?my Midwest rails are on my m5 308, and no problems, serving size 1, I’m not against other ideas for free float rails and barrel nuts. Just so far in my building experience I only run geissele rails or Midwest industries rails. I know that geissele barrel nut is bigger (thicker and longer) than the Midwest industries….I will never even consider rails without some sort of anti rotation tabs. Also seeking some clarification on the “tabbed gas block.”
Opinions from seasoned guys and personal experience welcome. hope y’all are having a good Wednesday. Most likely I’ll just grab more geissele rails, but was looking to save a little weight due to the already heavy barrel. And optic. God bless and semper fi

 

[TonyTheTiger]

I have no preference of 18” or 16”, was leaning towards 16” because I like the balance. And prefer short. But if there’s legit reasons to go rifle length gas and 18” over mid 16” please educate me.

Get the best of both worlds, 16" rifle gas. Or at least 16" intermediate.

If you shoot otherwise identical rifles, one mid gas and one rifle, you'll understand the benefits. If you reload and want to run hotter loads without killing brass, you'll see more benefits.
If you care about split times, you'll see benefits.

 

[bf2junky]

“Mk12 build” why even say that?

 

[Bacarrat]

“Mk12 build” why even say that?

Should change the title to "SPR Build"

If you are not going to have the major components that make it a MK12, don't call it as such.

 

[longshot2000]

“Mk12 build” why even say that?

Agree. As a builder of Mk12 rifles, not sure why you even are buying an SPR profiled barrel. The SPR profile is made to accept Ops, Inc. / Allen Engineering brake and collar to fit the AEM5 suppressor. If you are not wanting to shoot a Mk12, why try to change it.

But, one thing I would say, is that Centurion's roots are in the Mk12, as Monty was a Mk12 SEAL sniper. What he produces, in terms of rifles, barrels, receivers, rails, are his commercial version of what he would have liked to have shot. So, if you follow that logic, you can stay with Centurion and buy their parts and be very happy, especially as you mentioned that suppression was not a priority.

I am still wondering why you picked a Mk12 and then want to change everything...

We did a test on major SPR barrels a few years back, and most that advertised as Mk12 or SPR profile failed the test and would not adequately support the AEM5 suppressor. Not sure why. Allen's profile is in the public domain, so it is not hard to do it right, but the majority of barrels we tested failed the test. SO, It is a good thing that you are not looking to support a suppressor on the barrel you have chosen, as they did not meet the test when we tested, although, that might have changed.

If you like 16", then go for it. The Mod Holland Mk12 is a 16" barrel. The 18" rifle barrels have historically had early port erosion issues, whereas the 20" do not. In a visit a few years back with Frank White and Compass Lake, he showed me how much better the Douglass barrels held up to port erosion, compared to other barrels. But, as best we both can tell, Douglass is using the same 416R stainless steel, so not sure as to why. The port erosion issue I think has more to do with the shorter dwell time on an 18" barrel in rifle gas.

In theory, you will have the same issue with shorter dwell time with 16" barrel in intermediate length, but I have no empirical evidence to support that. The shorter dwell time is a somewhat newer preference for those shooting suppressed, and those in the know, like Bobby West at CGS suppressors, will swear by the most reduced dwell as possible when shooting suppressed.

So, you have a good barrel coming, and now you need to build around that. The rail choice will not affect accuracy. Get a rail that works for you. We tend to like Geissele, Midwest, LaRue, Centurion, to name a few. All of these will come in MLOK or railed, or a combination of both. Receivers are important, as is the BCG.

We tend to work with military correct receivers, so we have a few that are great, but I suppose I would expand on that list to include Vltor, which builds a ton of good stuff (just not military grade). You can also look at a Noveske Gen3 or Gen 4 receiver and rail. Great combo. Expensive. For BCG, we really like Microbest.

As a rifle builder, we have settled on Microbest as our premium in-house brand. Most of the better BCGs branded by other companies are Micobest. LMT and Geissele would be outliers as superior BCGs, but probably you are not going to see the difference in performance unless you run 15,000 rounds through your gun, and your barrel will be toast before then.

 

[bf2junky]

Agree. As a builder of Mk12 rifles, not sure why you even are buying an SPR profiled barrel. The SPR profile is made to accept Ops, Inc. / Allen Engineering brake and collar to fit the AEM5 suppressor. If you are not wanting to shoot a Mk12, why try to change it.

But, one thing I would say, is that Centurion's roots are in the Mk12, as Monty was a Mk12 SEAL sniper. What he produces, in terms of rifles, barrels, receivers, rails, are his commercial version of what he would have liked to have shot. So, if you follow that logic, you can stay with Centurion and buy their parts and be very happy, especially as you mentioned that suppression was not a priority.

I am still wondering why you picked a Mk12 and then want to change everything...

We did a test on major SPR barrels a few years back, and most that advertised as Mk12 or SPR profile failed the test and would not adequately support the AEM5 suppressor. Not sure why. Allen's profile is in the public domain, so it is not hard to do it right, but the majority of barrels we tested failed the test. SO, It is a good thing that you are not looking to support a suppressor on the barrel you have chosen, as they did not meet the test when we tested, although, that might have changed.

If you like 16", then go for it. The Mod Holland Mk12 is a 16" barrel. The 18" rifle barrels have historically had early port erosion issues, whereas the 20" do not. In a visit a few years back with Frank White and Compass Lake, he showed me how much better the Douglass barrels held up to port erosion, compared to other barrels. But, as best we both can tell, Douglass is using the same 416R stainless steel, so not sure as to why. The port erosion issue I think has more to do with the shorter dwell time on an 18" barrel in rifle gas.

In theory, you will have the same issue with shorter dwell time with 16" barrel in intermediate length, but I have no empirical evidence to support that. The shorter dwell time is a somewhat newer preference for those shooting suppressed, and those in the know, like Bobby West at CGS suppressors, will swear by the most reduced dwell as possible when shooting suppressed.

So, you have a good barrel coming, and now you need to build around that. The rail choice will not affect accuracy. Get a rail that works for you. We tend to like Geissele, Midwest, LaRue, Centurion, to name a few. All of these will come in MLOK or railed, or a combination of both. Receivers are important, as is the BCG.

We tend to work with military correct receivers, so we have a few that are great, but I suppose I would expand on that list to include Vltor, which builds a ton of good stuff (just not military grade). You can also look at a Noveske Gen3 or Gen 4 receiver and rail. Great combo. Expensive. For BCG, we really like Microbest.

As a rifle builder, we have settled on Microbest as our premium in-house brand. Most of the better BCGs branded by other companies are Micobest. LMT and Geissele would be outliers as superior BCGs, but probably you are not going to see the difference in performance unless you run 15,000 rounds through your gun, and your barrel will be toast before then.

Excellent post, great info.

 

[USMC-03XX]

I didn’t put the title as spr… Jesus Christ and thanks ? For the info? Not really. I’ve got google and know how to read, not to mention all the tier 1 guys I know and have trained and served with. Not to mention my vast personal experience and knowledge. But I forgot, I need to vet myself before asking a mass community of wannabes, for personal experiences. If you are just some civilian who builds guns, I don’t care what you think or your opinion. Guess I’ll just go with my own conclusions which were absolutely perfect without asking the peanut gallery. Nvm. You guys should just keep buying stuff based on the gear guys like me use. Make sure the exact nomenclature is followed or another internet geek will flex their nuts on you. I would almost bet my entire paycheck none of you have even pushed your AR’s past 500…. Or used any of your guns to shoot anything other than paper and animals.

 

[bf2junky]

I didn’t put the title as spr… Jesus Christ and thanks ? For the info? Not really. I’ve got google and know how to read, not to mention all the tier 1 guys I know and have trained and served with. Not to mention my vast personal experience and knowledge. But I forgot, I need to vet myself before asking a mass community of wannabes, for personal experiences. If you are just some civilian who builds guns, I don’t care what you think or your opinion. Guess I’ll just go with my own conclusions which were absolutely perfect without asking the peanut gallery. Nvm. You guys should just keep buying stuff based on the gear guys like me use. Make sure the exact nomenclature is followed or another internet geek will flex their nuts on you. I would almost bet my entire paycheck none of you have even pushed your AR’s past 500…. Or used any of your guns to shoot anything other than paper and animals.

Ohh boy!! Bruh no one gives a F who you trained with or what unit you served in. You are the one posting asking the peanut gallery for their thoughts.

“No one shot their AR past 500 yds” I’m at Arena multiple times a year

“Only punch paper or shoot animals” JFC I can’t…

 

[Bacarrat]

I didn’t put the title as spr… Jesus Christ and thanks ? For the info? Not really. I’ve got google and know how to read, not to mention all the tier 1 guys I know and have trained and served with. Not to mention my vast personal experience and knowledge. But I forgot, I need to vet myself before asking a mass community of wannabes, for personal experiences. If you are just some civilian who builds guns, I don’t care what you think or your opinion. Guess I’ll just go with my own conclusions which were absolutely perfect without asking the peanut gallery. Nvm. You guys should just keep buying stuff based on the gear guys like me use. Make sure the exact nomenclature is followed or another internet geek will flex their nuts on you. I would almost bet my entire paycheck none of you have even pushed your AR’s past 500…. Or used any of your guns to shoot anything other than paper and animals.

So you "know" tier 1 guys, and have a lot of "personal experience" but ask for build advice and also don't care for opinions from some dudes on the interwebs? lolwut?

So do you want my address now? Does shooting my MK12 to 1100 yards count?

 

[S197]

Get the best of both worlds, 16" rifle gas. Or at least 16" intermediate.

If you shoot otherwise identical rifles, one mid gas and one rifle, you'll understand the benefits. If you reload and want to run hotter loads without killing brass, you'll see more benefits.
If you care about split times, you'll see benefits.

16” rifle length gas can be picky.

 

[S197]

So to start off I’m not planning on ever running this suppressed. I have no preference of 18” or 16”, was leaning towards 16” because I like the balance. And prefer short. But if there’s legit reasons to go rifle length gas and 18” over mid 16” please educate me. Barrel is coming from centurion, my main question is about the barrel nut/handguard selection. I could care less about a true 100% clone. I don’t like quad rails, had them my entire career. Fat as fuxk. But that’s only because I’ve become spoiled with mlok since retiring. So my question is, if I run a Midwest industries rail vs a geissele rail, will it effect accuracy or reliability?my Midwest rails are on my m5 308, and no problems, serving size 1, I’m not against other ideas for free float rails and barrel nuts. Just so far in my building experience I only run geissele rails or Midwest industries rails. I know that geissele barrel nut is bigger (thicker and longer) than the Midwest industries….I will never even consider rails without some sort of anti rotation tabs. Also seeking some clarification on the “tabbed gas block.”
Opinions from seasoned guys and personal experience welcome. hope y’all are having a good Wednesday. Most likely I’ll just grab more geissele rails, but was looking to save a little weight due to the already heavy barrel. And optic. God bless and semper fi

Consider the nsw recce 15.1 style barrel. They can be built carbine or mid length. https://riflebarrels.com/shop/drop-in-barrels/ar/ar15/223/223-8-recce-m4-barrel-2/

below is my 14.5 mid length WOA

 

[TonyTheTiger]

16” rifle length gas can be picky.

That's what everyone says. Have you tried it?
After my 3rd or 4th trouble free 16" rifle gas barrel I got bored and tried a 14.8" rifle gas, and a 17" rifle +1", and I can't get any of those to be picky either.

 

[S197]

That's what everyone says. Have you tried it?
After my 3rd or 4th trouble free 16" rifle gas barrel I got bored and tried a 14.8" rifle gas, and a 17" rifle +1", and I can't get any of those to be picky either.

Yes, my factory late 90‘s bushmaster ran good, but i also ran a cut down 20” that would short stroke.

 

[MikeMiller]

So to start off I’m not planning on ever running this suppressed. I have no preference of 18” or 16”, was leaning towards 16” because I like the balance. And prefer short. But if there’s legit reasons to go rifle length gas and 18” over mid 16” please educate me. Barrel is coming from centurion, my main question is about the barrel nut/handguard selection. I could care less about a true 100% clone. I don’t like quad rails, had them my entire career. Fat as fuxk. But that’s only because I’ve become spoiled with mlok since retiring. So my question is, if I run a Midwest industries rail vs a geissele rail, will it effect accuracy or reliability?my Midwest rails are on my m5 308, and no problems, serving size 1, I’m not against other ideas for free float rails and barrel nuts. Just so far in my building experience I only run geissele rails or Midwest industries rails. I know that geissele barrel nut is bigger (thicker and longer) than the Midwest industries….I will never even consider rails without some sort of anti rotation tabs. Also seeking some clarification on the “tabbed gas block.”
Opinions from seasoned guys and personal experience welcome. hope y’all are having a good Wednesday. Most likely I’ll just grab more geissele rails, but was looking to save a little weight due to the already heavy barrel. And optic. God bless and semper fi

Sir
I have been shooting MK12’s since they came out. I have SPR rifles with 20”,18” and 16” barrels
Barrel length is important but quality of the barrel is a bigger deal. I look for one that gives me good accuracy with the most velocity of the length

I have routinely shoot to 1100 yards with 18” barrels and hot 77’s. 20” will give you a bit more velocity but I hate a 20” barrel in the field in 5.56

The 16” won’t keep up with the 18” for distance with both barrels being same quality

It was mentioned about Douglas. I was lucky enough to talk with one of the fathers of the MK12 project. He said Douglas was picked for barrel life and he reasoned the the buttoning hardened the steel so it fought erosion better. I don’t know they all seem to wear out about the same when they start equal quality to me but my sampling is far less than Cranes so I go with what they said

Lately I find myself in an area that does not lend itself to many shots past 700 yards so I like that 16” option if only one weapon but I have long been a fan of two
Uppers with short 13.5” mounted and 18” in ruck just in case I need more distance or parts

 

[S197]

Sir
I have been shooting MK12’s since they came out. I have SPR rifles with 20”,18” and 16” barrels
Barrel length is important but quality of the barrel is a bigger deal. I look for one that gives me good accuracy with the most velocity of the length

I have routinely shoot to 1100 yards with 18” barrels and hot 77’s. 20” will give you a bit more velocity but I hate a 20” barrel in the field in 5.56

The 16” won’t keep up with the 18” for distance with both barrels being same quality

It was mentioned about Douglas. I was lucky enough to talk with one of the fathers of the MK12 project. He said Douglas was picked for barrel life and he reasoned the the buttoning hardened the steel so it fought erosion better. I don’t know they all seem to wear out about the same when they start equal quality to me but my sampling is far less than Cranes so I go with what they said

Lately I find myself in an area that does not lend itself to many shots past 700 yards so I like that 16” option if only one weapon but I have long been a fan of two
Uppers with short 13.5” mounted and 18” in ruck just in case I need more distance or parts

Huh?

 

[MikeMiller]

Too broad a question but if you’re talking about barrel length. I have seen some really slow barrels and some fast barrels. Some 16” barrels are making more velocity than some 18” barrels so make sure you look at the quality and performance over the length. But with that said is the 16” and 18” are same quality you should get more velocity in the 18” than the 16”

My meaning of I want the highest velocity with good accuracy is simply put I prefer 2775 velocity and 1 moa groups over .75 moa and 2500 fps.

 

[USMC-03XX]

Sir
I have been shooting MK12’s since they came out. I have SPR rifles with 20”,18” and 16” barrels
Barrel length is important but quality of the barrel is a bigger deal. I look for one that gives me good accuracy with the most velocity of the length

I have routinely shoot to 1100 yards with 18” barrels and hot 77’s. 20” will give you a bit more velocity but I hate a 20” barrel in the field in 5.56

The 16” won’t keep up with the 18” for distance with both barrels being same quality

It was mentioned about Douglas. I was lucky enough to talk with one of the fathers of the MK12 project. He said Douglas was picked for barrel life and he reasoned the the buttoning hardened the steel so it fought erosion better. I don’t know they all seem to wear out about the same when they start equal quality to me but my sampling is far less than Cranes so I go with what they said

Lately I find myself in an area that does not lend itself to many shots past 700 yards so I like that 16” option if only one weapon but I have long been a fan of two
Uppers with short 13.5” mounted and 18” in ruck just in case I need more distance or parts

Thank you , I honestly stopped looking at this post because of the retarded responses I already over reacted to lol. I’m not really asking for anything other than personal experiences to help me reconfirm things I already know. I’ve been doing this for quite sometime not to mention it’s kind of a family legacy. If you were even halfway intelligent you would realize regardless of your opinions I have actually done these things in real life for many years. And have known and served with many other with even more time and experience than me. However I chosen to live off grid and I don’t have a cellphone.if that gives you any concept of my level of wanting to stay in touch with people. Just a wireless tablet. Zero social media. Just email, YouTube. Some shooting forums. So yeah part of my asking questions or posing ideas to a forum like this is also to help me pass time. BUT every so often I actually learn something.


ANYWAY… I decided to bite the bullet and go short. 16” mid gas. It’s fine for now, (temp) I decided to get a novekse barrel (416r), I plan on getting a Bartlein ordered or something similar (krieger). I got ahold of the guys at Douglas and they don’t make the AR spr barrels anymore but the gentleman gave me someone’s phone number who still makes them like Douglas used to? Something like that. I can go back and dig in my email if anyone wants more info on that. Oh and for anyone curious, PACNOR makes noveskes barrels still. I emailed pacnor and they explained that for a year after the fire, noveske had them made by someone else then they went back with pacnor once they had their new place up and running. I’m sure this is where the misconception that quality has “declined.” Some people say since John Novekse died, other when the pacnor facility burned. Regardless of any of this, I’m getting my nightforce NX8 2.5-20x50 for this upper and then I’ll order the barrel. I am grateful for the info! @MikeMiller

 

[MikeMiller]

Thank you , I honestly stopped looking at this post because of the retarded responses I already over reacted to lol. I’m not really asking for anything other than personal experiences to help me reconfirm things I already know. I’ve been doing this for quite sometime not to mention it’s kind of a family legacy. If you were even halfway intelligent you would realize regardless of your opinions I have actually done these things in real life for many years. And have known and served with many other with even more time and experience than me. However I chosen to live off grid and I don’t have a cellphone.if that gives you any concept of my level of wanting to stay in touch with people. Just a wireless tablet. Zero social media. Just email, YouTube. Some shooting forums. So yeah part of my asking questions or posing ideas to a forum like this is also to help me pass time. BUT every so often I actually learn something.


ANYWAY… I decided to bite the bullet and go short. 16” mid gas. It’s fine for now, (temp) I decided to get a novekse barrel (416r), I plan on getting a Bartlein ordered or something similar (krieger). I got ahold of the guys at Douglas and they don’t make the AR spr barrels anymore but the gentleman gave me someone’s phone number who still makes them like Douglas used to? Something like that. I can go back and dig in my email if anyone wants more info on that. Oh and for anyone curious, PACNOR makes noveskes barrels still. I emailed pacnor and they explained that for a year after the fire, noveske had them made by someone else then they went back with pacnor once they had their new place up and running. I’m sure this is where the misconception that quality has “declined.” Some people say since John Novekse died, other when the pacnor facility burned. Regardless of any of this, I’m getting my nightforce NX8 2.5-20x50 for this upper and then I’ll order the barrel. I am grateful for the info! @MikeMiller

Glad I could help